Bakelite line filter caps in 41-285 - Printable Version
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+--- Thread: Bakelite line filter caps in 41-285 (/showthread.php?tid=8760)
Bakelite line filter caps in 41-285 - Diverted - 02-11-2014
Hi all:
Newbie question. On chassis 41-285, why are the two .01 mfd line filter caps along the AC line installed in that odd grounded bakelite box, then buried in tar? I assume the best way to redo them is melt that goop and clear everything out? Do they need to stay in the box for some kind of shielding? Etc? Or can I mount new caps outside it? Thanks,
Ted
RE: Bakelite line filter caps in 41-285 - skyscraper - 02-11-2014
Philco put capacitors in those blocks, and filled them with tar. It gave them mounting points for other wires and made the chassis cleaner. I have no idea why they had to use tar...
Those two caps filter out noise in the AC line, and give you a cleaner power supply. Each goes to one leg of the line and ground. They should technically be safety caps, but regular ones are usually fine. http://www.justradios.com/safetytips.html
To remove the tar 'plug', cut the four little wires in the rivet holes on the top of the block (I use a razor blade), then heat it with a heat gun on the top and sides. After 20 seconds, use a small screwdriver to push the contents out the bottom. It is a much better idea to mount them inside the old block, both for safety and aesthetics.
Over at the Philco Repair Bench there are articles about the contents and connections of various blocks, and how to restuff them.
RE: Bakelite line filter caps in 41-285 - morzh - 02-12-2014
In addition to what Skyscraper has noted,
1. heat on "Low" using a heatgun. In case you do not have "Low" (some heatguns have cool and hot, and some Low and High) use high from a distance. I use "Low" for 10-15 sec, equal time every side.
2. Use a blunt instrument like a small Allen wrench. Sometimes the tool gets in between the two caps that are inside and if it is any sharp it can cut through the warm tar and you get a hole and the tar block still stays inside.
3. If it resists, heat one more time, do not force much.
4. Leave the cap in place (do not unscrew) when you do it and do not unsolder the wires - makes it so much easier, just cut the think wires coming from inside the block (!!!! - very important unless you want to deal with a mess).
5. No regular caps are NOT fine. Use only Y-rated capacitors.
RE: Bakelite line filter caps in 41-285 - Raleigh - 02-12-2014
I'm no expert, but I think Philco potted the caps to keep any moisture from degrading the line filter caps. Since they were connected line to ground, they'd have more catastrophic effects if they shorted or leaked than most other caps in the chassis.
I use X/Y caps from Just Radios, which are disk-shaped. They fit fine, except they stick out the open bottom of the Bakelite box just a tiny bit, not enough to see or to interfere with the fit.
Most of us leave the Bakelite block in place after replacing the caps because it's a convenient place to connect AC and transformer lines to those filter caps, and to connect one or two things nearby to ground. You could do the same thing with a terminal strip, I suppose, but the Bakelite shell looks good.
RE: Bakelite line filter caps in 41-285 - morzh - 02-12-2014
"Catastrophic" meaning "becoming the death cap" if someone touched the chassis and Earth at the same time.
RE: Bakelite line filter caps in 41-285 - klondike98 - 02-12-2014
Hi Ted welcome to the Phorum. Some Bakelite block cap info that you will find useful can be found here: http://www.philcoradio.com/tech/blocks.htm . A tutorial on X and Y safety caps can be found here: http://www.justradios.com/safetytips.html
RE: Bakelite line filter caps in 41-285 - TV MAN - 02-12-2014
Ted, check out my bakelite cap rebuild in the thread "70 rebuild". I just finished those and have a few pics posted. Also some useful info in "70 restoration" thread by "morzh".
RE: Bakelite line filter caps in 41-285 - Diverted - 02-13-2014
thanks!